Ballistics Momentum problem

In a ballistics test, a 25.0g bullet traveling horizontally at 1100m/s goes through a 40.0cm -thick 250kg stationary target and emerges with a speed of 900m/s . The target is free to slide on a smooth horizontal surface.

the 1st question of this problem ask: How long is the bullet in the target?

In a ballistics test, a 25.0g bullet traveling horizontally at 1100m/s goes through a 40.0cm -thick 250kg stationary target and emerges with a speed of 900m/s . The target is free to slide on a smooth horizontal surface.

the 1st question of this problem ask: How long is the bullet in the target?